Overhead electric power lines, wires or cables are supported by poles or towers which may be constructed of wood, metal or other construction materials. The overhead power liens are mounted on the poles or towers by insulators which are maintained upright by an upstanding pin engaged in an axial blind bore of the insulator body.
These insulators were, in the past, typically constructed of a ceramic material such as porcelain, and have a variety of shapes and/or designs depending upon the necessary mechanical strength, dielectric strength and leakage distance. However, the use of porcelain for insulators has several disadvantages. For example, porcelain insulators are often very heavy to provide the necessary mechanical and electrical characteristics. Moreover, such porcelain insulators are typically expensive to install and require strong supporting structures. Additionally, porcelain insulators are brittle, and thus, subject to being damaged during shipping and installation. Porcelain insulators are also susceptible to vandalism damage.
Accordingly, in recent years, newer insulators have been developed which include a fiberglass reinforced polymer core and an external protective housing forming annular flanges and webbed weathersheds. The weathershed housing or sheath is usually made of an elastomeric or an epoxy material. Elastomer or epoxy sheaths are designed to protect the fiberglass reinforced cores from weather and electrical activity. Weather and electrical activity degrade the mechanical strength of the fiberglass reinforced cores. The weathersheds on the housing intercept water flow down the insulators and increase the distance along the surface of the insulator for better electrical performance in wet or contaminated conditions.
With use of a dielectric polymer core, significant stresses, particularly electrical stresses, are created between the line wire and the ground insert coupled to the insulator. Additionally, the use of externally mounted clamps hinders installation and increases the cost of the components.